Agrowtek RD8i Relay Module
Eight-channel dry-contact relay module for lighting, ventilation, irrigation and HVAC.
The Agrowtek RD8i is a relay module with eight dry contacts that switches lights, fans, heaters, irrigation pumps and dehumidifiers in greenhouses and indoor farms. This Modbus RTU template reads the state and closure count of every relay through the LX2 ModLINK, and lets you switch the relays and set the communication timeout from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 23, read and write
- Brand
- Agrowtek
- Key readings
- Relay contact states · Closure count per relay · Communication timeout
- Available commands
- Relay on and off · Communication timeout · Modbus address
- Compatible models
- RD8i · RD8i+
- Last updated
Registers (23)
23 read, 10 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Relay 1 | Read and write | ||||
| Relay 2 | Read and write | ||||
| Relay 3 | Read and write | ||||
| Relay 4 | Read and write | ||||
| Relay 5 | Read and write | ||||
| Relay 6 | Read and write | ||||
| Relay 7 | Read and write | ||||
| Relay 8 | Read and write | ||||
| Communication Timeout | s | Read and write | |||
| Relay 1 Closure Count | Read | ||||
| Relay 2 Closure Count | Read | ||||
| Relay 3 Closure Count | Read | ||||
| Relay 4 Closure Count | Read | ||||
| Relay 5 Closure Count | Read | ||||
| Relay 6 Closure Count | Read | ||||
| Relay 7 Closure Count | Read | ||||
| Relay 8 Closure Count | Read | ||||
| Device Address | Read and write | ||||
| Serial Number | Read | ||||
| Date of Manufacture | Read | ||||
| Hardware Version | Read | ||||
| Firmware Version | Read | ||||
| Device Model | Read |
Loading registers…
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Show which of the eight relays are on for lights, fans and pumps on one ModbusCloud dashboard.
- Switch a relay from the portal, for example to start an extra fan or an irrigation pump.
- Use an automation that switches a relay on a schedule or when a temperature from a climate sensor crosses a threshold.
- Track the closure count per relay to plan replacement before the rated 100,000 cycles.
- Get an email or webhook each time a relay changes state, with a rule on the change condition.
Installation
Mount the RD8i and wire the loads to the dry contacts, up to 3.5 A at 120 Vac or 24 Vdc per contact.
Connect the GrowNET port to an Agrowtek LX2 ModLINK, directly or through an HX8 hub, and wire TX/RX+ and TX/RX- of the LX2 to the RS485 terminals of the ModbusCloud Gateway. Terminate the bus.
Give the module its own address from 1 to 247 with the AgrowLINK utility, or write it to the address register at broadcast address 254 while it is the only device on the bus.
In ModbusCloud, add a Modbus device with protocol RTU, the address, 19200 baud, 8 data bits, no parity and 1 stop bit, and import this template.
Check the relay states. Before you switch relays from the portal, set the timeout longer than the read interval of the Modbus device.
Things to watch for
The relay module does not answer through the LX2. What should I check?
Check 19200 baud, no parity, 1 stop bit and the module address in ModbusCloud; the LX2 may have been set to another speed with the ModLINK utility. Swap TX/RX+ and TX/RX- if nothing comes back, terminate the RS485 bus, and give every GrowNET device behind the LX2 its own address.
The relays switch off on their own. Why?
Check Communication Timeout: the RD8i turns the relays off when the master sends nothing for that many seconds. If ModbusCloud reads the module less often than that, the relays drop out between reads. Set the timeout longer than the read interval of the Modbus device.
A relay clicks and its LED is on, but the load does not run.
Check for continuity across the contact while the relay is on. If it conducts, the fault is in the load or its power source, not in the relay. Overloading a contact can burn or weld it, so stay below 3.5 A per point.
How do I switch a relay from ModbusCloud?
Write 1 to the relay coil to close the contact and 0 to open it. On an RD8i with manual toggles, a switch that is not in the centre position overrides the controller. Writing is off per gateway by default; request it for the gateway in the portal.
Can I plug the GrowNET cable into the network port of the Gateway?
No. GrowNET uses RJ45 plugs but it is not Ethernet. Connect the module to the LX2 ModLINK and wire the LX2 to the RS485 terminals of the ModbusCloud Gateway.
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